Since I have a lot of different Genres, changing them by hand would require too much effort, so I have written a very small utility, which does that for me. Since it seems to be stable and worked for my collection, I'd be happy to share it with you guys. I uploaded the C++- source code to your FTP-Server:

What it simply does is parse the XML-structure of the TrackList.xml and replaces the Genre Numbers by the according Genre String according to the Id3-Spec. The output is written into a new XML-File, which can be re-scanned by Mede8er.